warning preg_replace Unknown modifier errors

Unfortunately I have no way to test the module on a php 5 environment. But it might help if you tell me what string did you want to replace. Cause that errors tells me that you have some non alpha numeric characters. I think you use "/" somewhere in the string, but I might be wrong.

Alinks was at first designed to work with single words. I think it's impossible to make it work on any string. I can do that, but the option to limit the instances replaced will be lost (but if I use str_replace instead of preg_replace then the "plural problem" will appear again).
@capmex
I'm actually amazed that "Alert!" works. "Better Homes & Gardens" doesn't work cause "&" it's replaced with "&" when submitting the article.
I made some test and until now, if I add an option to alinks so you can choose if the string is a "word" or not you can make some of your example work. I couldn't make $25 Coupon and Alert! to work even with this enabled. If instead of "$25 Coupon" I use "A $25 Coupon" it works (with the changes I've made).
The fact is that now alinks doesn't work on strings that start or end with anything else than a letter, number or underscore character or with strings that have "/" (the character I used as delimiter).
@midkemia
The changes made from version 1.0 can be problematic if you have text like this "". Cause anything inside "<" and ">" will be stripped out if you don't use "<" and ">" respectively to write those characters.

I've made some more testing.
For those familiar to regular expressions. As is now, alinks looks both at start and at the end of the string for a "word boundary" (a alphanumeric or underscore character).
The solution, as I see it now, is to add two check boxes (one for the start of the string and one for the end of the string) so that the administrator can "tell" if those are "word boundary" (so if the check box is enabled is not a word boundary).
Now I want your opinions on that, if it's clear enough and easy to use for a regular site webmaster, and not for experts. I will make the required changes and submit a patch so you can test it and maybe share your experience with it.

Download the latest version and let me know what you think about this.

In post #8 what I meant was that & is replaced with &
I must agree with midkemia, the purpose of this module is to automatically replace strings inserted by users. It's not to replace strings like The World Is Flat [Updated and Expanded]. What's the probability that a user writes this string exactly like that? It seems to me that is used for a site design problem (to replace that string in a limited number of pages designed by the site webmaster). But non the less I will let this option enabled. I think that I'll add an option for advanced alinks, so if you enable that you see the boundary option, if not you don't.
I also think I have to add the restrictions to the module description cause as I see people expects from this module more that is designed to do.

I don't know if this is still active, but that preg_replace() Unknown identifier error can be solved with preg_quote(). What ever string is being matched, say preg_replace("/" . $match . "/","whatever",$string), the $match variable may have regular expression special characters, so you can escape them with preg_quote(). If you're delimiter is / like in the example, just use preg_replace("/" . preg_quote($match,"/") . "/","whatever",$string).

That should do it, let me know if you have questions.